Using the Sun to estimate Earth-like planets detection capabilities IV. Correcting for the convective component
Using the Sun to estimate Earth-like planets detection capabilities IV. Correcting for the convective component
复制标题
利用太阳估计类地行星探测能力 IV．
DOI：
10.1051/0004-6361/201219917
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发表时间：
2013
影响因子：
6.5
通讯作者：
A. Lagrange
中科院分区：
文献类型：
--
作者：
N. Meunier;A. Lagrange
上下文径向速度（RV）的时间序列强烈影响恒星活动的存在。在一系列的论文中，我们已经重建了太阳RV的变化，在一个完整的太阳周期，从观察到的太阳结构（斑点和plages），并研究了它们对地球质量的行星在太阳的可居住区的可探测性的影响，从邻居星星在几个典型的情况下。我们发现，对流的贡献占主导地位的RV时间序列。目标。本文的目的是双重的：确定检测限的太阳一样的星星看到不同程度的对流和估计的性能的活动校正使用钙指数。方法.我们采用两种方法来计算检测限：基于相关性的方法和局部功率分析方法，这两种方法都考虑到了观测的时间结构。此外，我们测试了两种方法，使用Ca指数来校正对流对RV的贡献：Ca变化的正弦拟合和RV-Ca关系的线性拟合。在这两种情况下，我们使用观察到的Ca和重建的Ca来研究我们估计的各种影响和局限性。结果我们确认，在没有对流和低RV噪声的情况下，必须进行出色的采样，以使检测限低于1 MEarth（例如0.2−0.3 MEarth）。在对流情况下，检测限始终高于7 MEarth。当Ca时间序列有噪声时，这两种校正方法的性能相似，导致显著改善（下降到几个MEarth），高于1个MEarth限制。在非常好的Ca噪声（信噪比，S/N，大约130）的情况下，正弦方法并没有变得明显更好，因为它受太阳周期不是正弦的事实支配，但是RV-Ca方法可以达到1 MEarth以获得优异的Ca噪声水平。结论.对于类太阳的条件下，考虑简化的假设，我们首先得出结论，几个MEarth行星的检测极限可以达到提供良好的采样和钙噪声。1 MEarth的检测可能是可能的，但只有具有良好的时间采样和良好的Ca指数噪声水平：我们估计，在1.2 Au检测到1 MEarth的概率大于50%，需要超过1000个良好采样的观测值和大于130的Ca S/N。
Context. Radial velocity (RV) time series are strongly impacted by the presence of stellar activity. In a series of papers, we have reconstructed solar RV variations over a full solar cycle from observed solar structures (spots and plages) and studied their impact on the detectability of an Earth-mass planet in the habitable zone of the Sun as seen edge-on from a neighbour star in several typical cases. We found that the convective contribution dominates the RV times series. Aims. The objective of this paper is twofold: to determine detection limits on a Sun-like star seen edge-on with different levels of convection and to estimate the performance of the activity correction using a Ca index. Methods. We apply two methods to compute the detection limits: a correlation-based method and a local power analysis method, which both take into account the temporal structure of the observations. Furthermore, we test two methods using a Ca index to correct for the convective contribution to the RV: a sinusoidal fit to the Ca variations and a linear fit to the RV-Ca relation. In both cases, we use observed Ca and reconstructed Ca to study the various effects and limitations of our estimations. Results. We confirm that an excellent sampling is necessary to have detection limits below 1 MEarth (e.g. 0.2−0.3 MEarth) when there is no convection and a low RV noise. With convection, the detection limit is always above 7 MEarth. The two correction methods perform similarly when the Ca time series are noisy, leading to a significant improvement (down to a few MEarth), which is above the 1 MEarth limit. With a very good Ca noise (signal to noise ratio, S/N, around 130), the sinusoidal method does not get significantly better because it is dominated by the fact that the solar cycle is not sinusoidal, but the RV-Ca method can reach the 1 MEarth for an excellent Ca noise level. Conclusions. For Sun-like conditions and under the simplifying assumptions considered, we first conclude that the detection limit of a few MEarth planet can be reached providing good sampling and Ca noise. The detection of a 1 MEarth may be possible, but only with an excellent temporal sampling and an excellent Ca index noise level: we estimate that a probability larger than 50% to detect a1 MEarth at 1.2 AU requires more than 1000 well-sampled observations and a Ca S/N larger than 130.